The concept of current limiting, wherein the circuit is interrupted in the early stages of the current waveform, has resulted in corresponding reduction in the size of the components used to carry circuit current within the circuit interruption device. The rapid separation of the contacts within the device to achieve such current limiting, however, interrupts the circuit at the later stages of the voltage waveform, thereby requiring sophisticated arc-extinguishing apparatus. U.S. Pat. No. 4,375,021, entitled "Rapid Arc Extinguishing Assembly In Circuit Breaker Devices Such As Electric Circuit Breakers", describes the use of a high speed magnetically driven contact assembly to limit circuit current during the interruption process. The complex arc chute assembly described within this patent for cooling and extinguishing the arc that occurs during such rapid interruption adds to the economics of the breaker design.
The use of a voltage-dependent element such as a varistor electrically connected in parallel with a pair of separable contacts to absorb the system energy and to reduce arcing is described, for example, within U.S. Pat. No. 3,543,047, entitled "Contact Arc Suppressor Using Varistor Energy Absorbing Device". This patent concerns circuit interruption devices involved in relatively low energy electronic circuits. An early attempt to employ voltage dependent elements for arc suppression within molded case circuit breaker devices, such as used within residential and industrial power distribution systems, is described within U.S. Pat. No. 2,753,423, entitled "Arc Suppressors For Electric Switch Gear", discloses an arc chute made of a semi-conducting material that decreases in resistance upon reaching a predetermined voltage.
It has since been determined that the size of the arc chute required for cooling and extinguishing arcs that are created by high speed current limiting circuit interrupts can be effectively reduced by means of a combination metal plate-varistor arc chute wherein the metal plates serve to attract the arc to the varistors which, when conductive, quench the arc and, in time, become heated in the process. The metal plates then serve to effectively cool the varistors once the arc has been extinguished.